Flame-resistant cellulosic fiber, its use and production process

ABSTRACT

The present invention relates to a flame-retardant cellulosic regenerated fiber for textile applications which for example also satisfies the demands of industrial dry cleaning, its use for the production of yarns and fabrics and a process for the production of these fibers.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to flame-resistant cellulosic regenerated fibers with enhanced usability properties for textile applications which for example also satisfy the requirements of industrial dry cleaning, their use for the production of yarns and fabrics and a process for the production of these fibers.

2. Description of Related Art

Today above all fibers according to the viscose process are known as cellulosic regenerated fibers and they are made around the globe for standard applications in the textile and non-wovens sector with an individual fiber titer of between 0.8 and 16 dtex. Different chemicals are described in the literature for the flame-resistant finishing of viscose fibers. In this respect flame-protection agents are used on the basis of halogens, silicium and phosphorous.

In U.S. Pat. No. 2,678,330, the use of Bis(2,3 dichloroproply)chlorophosphonate is described for the purpose of this application. The publication GB1158231 mentions the use of a Tris(1-bromo-3-chloro-2-proply)phosphate. Patent FR2138400 describes the use of liquid polybromobenzene and in particular and preferably hexabromobenzene. Since liquid flame-resistant agents are only embedded in the structure of the fiber, but do not build up a covalent bond to the cellulose component, the migration of these chemicals from the fiber is much higher than with solid substances. Above all after repeated drying at high temperatures (e.g. in a tunnel drier) the flame-resistant property of the fiber can be clearly reduced.

Likewise Soviet patent SU661047 describes the use of halogenated compounds such as hexachlorocyclohexan, halogenated benzene and Tris(dibromopropyl)-phosphate. The use of a flame-resistant agent containing halogen was greatly reduced in recent years due to ecological considerations and does not represent a sustainable solution for future developments. Tris(dibromo-propyl)phosphate is for example listed by the Oeko-Tex® community as a prohibited flame-resistant agent.

Viscose fibers, the flame-resistant effect of which is based on the use of silicates—described for example in patents WO9313249 or CN1847476—are ecologically harmless but do not at all meet the requirements of the modern textile industry with regard to the mechanical fiber properties and washing fastness. According to the present day level of knowledge, only completely water-insoluble solid flame-resistant agents containing phosphorous, which contain no halogens, can fulfill all the demands made in terms of ecology, flame-resistant behavior, the textile data and other usability properties.

Patent EP0836634 describes a flame-resistant regenerated fiber produced according to the Lyocell process and which would theoretically fulfill the demands named above. The production of the phosphorous compound used there is, however, not possible on a large scale and, therefore, too expensive so that this fiber does not represent an alternative for conditions in practice.

The production of flame-resistant viscose fibers based on the incorporation of a pigment containing phosphorous in a standard viscose process is also described in the Chinese patents CN 101215726, CN101037812 and CN1904156. The fibers described in these patents do not, however, satisfy the high demands of the modern textile industry and their customers as is shown later on the basis of tests (table 1).

Patents DE4128638A1 or DE102004059221A1 describe flame-resistant dispersion media on the basis of a 2,2′-oxybis[5,5-dimethyl-1,3,2 dioxaphosphorinane]2,2′ disulfide using different dispersion medium systems and also mention the use of these dispersion media for the flame-resistant finishing of viscose fibers.

Likewise EP1882760 describes the production of flame-retardant viscose fibers using flame-protection dispersion media on the basis of a 2,2′-oxybis[5,5-dimethyl-1,3,2 dioxaphosphorinane]2,2′ disulfid. Here the fact that the particle size may equal a maximum of 10 μm is described as the most important characteristic of the invention and that the spinning mass, therefore, has to be cleaned before spinning through filters with a maximum aperture width of 10 μm. It has, however, be seen that this criterion does not suffice to produce fibers which satisfy the demands described here. The maximum particle size described in EP1882760 of 10 μm is perhaps sufficient for viscose filaments i.e. endless filaments but it does not in any way satisfy the requirements of modern staple fiber production with fiber finenesses of approx. 1 to 4 dtex; a 1.3 dtex fiber has a diameter of approx. 10 μm.

Today standard viscose fibers are used to a large extent for lightweight fashionable textiles. The low tenacity, above all in the wet condition, the high elongation and the high area shrinkage do however place restrictions on the use of viscose fibers. These textile properties do not for example allow for the use in segments, which demand frequent washing of the textiles (particularly in industrial laundries). A measurement of the washing suitability is for example the area shrinkage. To be able to easily record the area shrinkage in quantitative terms, the correlation with the wet modulus, measured according to the regulations of BISFA and thus in the following simply referred to as the “BISFA wet modulus” (BISFA, testing methods viscose, Modal, Lyocell and acetate staple fibers and tows, 2004 Edition), is used.

The correlation between area shrinkage (after washing) and the BISFA wet modulus has been known for viscose fibers since the 70's of the last century (Szegö, L., Fiber Research, Text. Techn.; 21(10), 1970). With a BISFA wet modulus of 2, one can assume a washing shrinkage of 15-20%, with a BISFA wet modulus of 5 the shrinkage already drops to 4-7% (see FIG. 1).

The fibers described in the state of the art, or commercially available, are all produced by standard viscose processes. They show by comparison good mechanical fiber data for flame-resistant viscose fibers since the phosphorous contents are very low. Tests with a variety of flame-protection agents on the basis of phosphorous have, however, shown that a sufficient flame-resistant effect is achieved as of a phosphorous content of more than 2.8%. The flame-protection capability correlates very well with the content of flame-protection agent converted to pure phosphorous.

However, it could be ascertained that for example the incorporation of large amounts (15-25%) of a flame-resistant pigment leads to a further deterioration of the textile parameters of the viscose fiber. For this reason the restriction for the applications already mentioned for standard viscose fibers apply even more so to the flame-resistant viscose fibers.

This is even more regrettable since flame-resistant fibers could be used to particular advantage in products which are also exposed to strong mechanical loads, for example in professional clothing for particularly dangerous activities in fire brigades, casting mills, the armed forces, the oil and chemical industry. For products of this kind, synthetic high-performance fibers such as (aromatic) polyamides, aramides, polyimides and similar products are normally used. However, these fibers have a low wear comfort since they are not able to absorb moisture to a sufficient extent. A blend of these fibers with cellulosic fibers, which add enhanced wear comfort to the range of properties, without otherwise drastically deteriorate the other properties, would therefore be desirable.

To sum up, the state of the art only discloses flame-resistant fibers which were either produced with ecologically harmful chemicals, do not have a sufficient tenacity, BISFA wet modulus and textile usability properties, cannot be used for textile purposes due to their mode of production or cannot be produced on a large scale. In actual fact some publications reveal nothing other than the intention of the editor to wish (also) to be able to produce flame-resistant cellulosic fibers.

Task:

Compared to the state of the art, the task was to make a flame-resistant cellulosic fiber available which satisfies today's requirements with regard to an economically and ecologically responsible production process and the higher textile mechanical requirements such as for example when industrially dry cleaning the articles of clothing produced in this way.

The demands of a flame-resistant fiber for modern textile applications can be described in practical terms by the product with a phosphorous content (this complies with the flame-resistance capacity) and a wet modulus, measured according to the regulations of BISFA (correlates with the area shrinkage). The product with a phosphorous content and BISFA wet modulus is therefore to be designated in the following as the “usability value”.

In addition the task involved making a suitable production process available for these fibers.

SUMMARY OF THE INVENTION

Surprisingly it was possible to solve this task by a flame-resistant regenerated cellulose fiber for textile applications which contains an incorporated, particle-shaped phosphorous compound as a flame-resistant substance, preferably an organophosphorus compound and a usability value of between 6 and 35, preferably between 8 and 35 and most preferably between 10 and 35. It was possible to produce a fiber of this kind for the first time by means of a viscose process modified in accordance with the invention.

BRIEF DESCRIPTION OF THE FIGURES

For a more complete understanding of the present invention, and the advantages thereof, reference is made to the following descriptions taken in conjunction with the accompanying figure, in which

FIG. 1 is a graph showing the correlation between area shrinkage (after washing) and the BISFA wet modulus for viscose fibers; and

FIG. 2 is graph showing suitable size distributions for pigment dispersions in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

This flame-resistant substance preferably has a particle size distribution with an X₅₀ value of less than 1.0 μm and an X₉₉ value of less than 5.0 μm.

By preference 2,2′-oxybis[5,5 dimethyl-1,3,2 dioxaphosphorinane]2,2′ disulfid (formula 1) is used as the organophosphorus compound. Sufficient quantities of this substance are among other things available under the trading name of Exolit® and Sandoflam® and this is also not washed out of the production process when being applied later:

The fiber according to the invention contains at least 2.8%, in a preferred embodiment of the invention preferably between 3.2% and 6.0%, and most preferably between 3.5% and 6.0% of phosphorous in relation to cellulose. Lower contents of phosphorous than 2.8% do not produce a sufficient flame-resistant effect. Higher contents of phosphorous than 6% reduce the mechanical properties of the fibers and are, moreover, no longer economical.

A flame-resistant fiber in accordance with the invention is particularly suited which has a BISFA wet modulus B_(m) of more than or equivalent to 0.5·(√T)·10/T with an elongation of 5% in the wet state. In this T is the titer of an individual fiber, expressed in dtex; B_(m) is expressed in cN/tex. The fiber in accordance with the invention is preferably in the form of a staple fiber i.e. it is cut to a unified length within the course of the production process. Usual cut lengths for staple fibers for the textile field lie between approx. 20 and 150 mm. Only a unified length like this of all of the fibers allows for non-problematic processing on the machines common today in the textile chain with a high productivity.

The subject matter of the present invention is also the use of a fiber in accordance with the invention for the production of a yarn. A yarn like this is characterized by a much higher strength compared to yarns of the fibers which were available until now. In order to be able to reveal suitable properties for the respective application, a yarn like this in accordance with the invention can, in addition to the fibers in accordance with the invention, also contain fibers of another origin, for example wool, flame-resistant wool, para and meta aramides, polybenzimidazole (PBI), p-phenyl-2,6-bezobisoxazole (PBO), polyimide (P84®), polyamide-imide (Kermel®), modacryl, polyamide, flame-resistant polyamide, flame-resistant acrylic fibers, melamine fibers, polyester, flame-resistant polyester, polyphenylene sulphide (PPS), polytetrafluorethylene (PTFE), glass fibers, cotton, silk, carbon fibers, oxidized thermally stabilized polyacrylnitrile fibers (PANOX®) and electrically conductive fibers and blends of these fibers.

Likewise the use of the fiber in accordance with invention for the production of a fabric is the subject matter of the present invention. Additionally to the fibers in accordance with the invention, this fabric can also contain other fibers, for example and in particular wool, flame-resistant wool, para and meta aramides, polybenzimidazole (PBI), p-phenyl-2,6-bezobisoxazole (PBO), polyimide (P84®), polyamide-imide (Kermel®), modacryl, polyamide, flame-resistant polyamides, flame-resistant acrylic fibers, melamine fibers, polyester, flame-resistant polyester, polyphenylensulphide (PPS), polytetrafluorethylene (PTFE), glass fibers, cotton, silk, carbon fibers, oxidized thermally stabilized polyacrylnitrile fibers (PANOX®) and electrically conductive fibers and blends of these fibers.

The fabric is preferably a woven fabric, hosiery fabric or knitted fabric, but it can basically also be a non-woven. Likewise for high-quality non-wovens, the use of fibers with a high BISFA wet modulus and a high strength is of decisive importance. In the case of a woven or knitted fabric, the blend of fibers in accordance with the invention with the other fibers is possible either by blending prior to the production of the yarn, a so-called intimate blend, or by the joint use of in each case pure yarns of the different fiber types when weaving, warping or knitting.

The fiber in accordance with the invention can be produced using a viscose process in accordance with the invention and modified which is likewise the subject matter of the present invention. Viscose processes for staple fibers and endless filaments have principally been known for many years and are for example described in detail in K. Götze, Chemiefasern nach dem Viskosefasern, 1967. The textile properties of the fibers and filaments obtained from this are, however, considerably influenced by many parameters. In addition, limits are stipulated for many of the influencing variables due to the design of the existing production units, which can for technical or economic reasons, not be surpassed so that various variations of the parameters are often not possible and the specialist is not even called upon to do this.

It has been seen that for the production of the fibers in accordance with the invention, a cellulose concentration of 4-7% when using a pulp with an R-18 content of 93-98% and an alkali ratio (cellulose concentration/sodium hydroxide concentration, always in g/l) of 0.7 to 1.5 represent the ideal conditions. However, the spinning parameters must be correspondingly adapted due to the adding of the flame-resistant FR pigment.

The subject matter of the invention is, therefore, also a process for the production of a flame-resistant regenerated cellulose fiber for textile applications by spinning a viscose with a content of 4 to 7% cellulose, 5 to 10% NaOH, 36 to 42% (in relation to cellulose) carbon disulphide and 1 to 5% (in relation to cellulose) of a modification agent into a spinning bath, drawing off the coagulated threads, whereby a viscose is used the spinning gamma value of which is 50 to 68, preferably 55 to 58, and the spinning viscosity of which equals 50 to 120 ballfall seconds; and that the temperature of the spinning bath equals 34 to 48° C. whereby

A) The alkali ratio (=cellulose concentration/alkali content) of the viscose ready for spinning equals 0.7 to 1.5,

B) The following spinning bath concentrations are used:

H₂S0₄ 68-90 g/l Na₂S0₄ 90-160 g/l ZnS0₄ 30-65 g/L

C) The final draw-off from the spinning bath takes place at a speed of between 15 and 60 m/min and

D) a particle shaped organophosphorous compound in the form of a pigment dispersion is incorporated as the flame-resistant substance.

It makes sense to use a viscose where the modification agent is added to the viscose shortly before spinning.

The measures suggested in accordance with the invention of adhering to a certain spinning maturity, for which the spinning gamma value is characteristic, of adhering to a certain viscosity, for which the ballfall values are characteristic, and of adhering to certain conditions in the spinning bath, altogether lead to the requested fiber properties. By the spinning gamma value, one understands the share of carbon disulphide molecules bound to 100 cellulose molecules. The spinning gamma value is determined in accordance with Zellcheming-data sheet draft of R. Stahn [1958] respectively sheet III/F 2. The ballfall value stands for the viscosity determined according to the ballfall method; this is expressed in ballfall seconds. The definition is provided in K. Götze, Chemiefasern [1951], p. 175.

The flame-resistant phosphorous compound, which is made as a pigment, is added to the viscose spinning solution in the form of a pigment dispersion. In this respect so much of the flame-resistant substance is incorporated that the finished fiber contains at least 2.6%, preferably between 3.2% and 6.0%, and most preferably between 3.5% and 6.0% of phosphorous, in relation to cellulose.

As already mentioned further above, a particularly suitable flame-resistant organophosphorus compound for the purposes of the present invention is the 2,2′-oxybis[5,5-dimethyl-1,3,2-dioxaphosphorinane]2,2′ disulphide.

In particular the quality of the pigment dispersion has a considerable influence on the fiber properties. This is determined by the average and maximum particle size of the pigments, the concentration of the dispersion in use, i.e. when adding to the viscose spinning solution, and the type and amount of the dispersing agent.

In comparison to the upper particle size of 10 μm described in patent EP1882760, it was found that an average particle size (_(x50)) of less than 1 μm and a maximum particle size (_(x99)) of less than 5 μm are necessary. FIG. 2 shows a size distribution of a pigment dispersion still suitable.

Preferably the pigment dispersion should contain between 10 and 50% of the flame-resistant substance.

In most documents on the state of the art, the influence of the dispersing agent is not described in as much detail as would seem appropriate. Lots of chemicals which supply an excellent stabilized flame-resistant pigment dispersion do, however, have a negative effect on the spinning process since they also lead to a modified effect in the viscose thread but do not have a positive influence on the fiber tenacity in comparison to the modifying agents used. The dispersing agents which have turned out to be best for the flame-resistant pigment dispersions for the production of fibers in accordance with the invention, which do not have a negative influence on the fiber strength, are those from the group containing modified polycarboxylates, water-soluble polyester, alkyl ether phosphates, end-capped nonoxynols, recinus oil alkoxylester and carboxymethylated alcoholpolyglycolether. Preferably the pigment dispersion should contain between 1.5 and 13% of the dispersing agent.

The invention is now to be explained using examples. These are to be understood as possible embodiments of the invention. In no way is the invention restricted to the scope of these examples.

EXAMPLES Example 1

6 weight parts 2,2′-oxybis[5,5-dimethyl-1,3,2-dioxaphosphorinane]2,2′ disulfide, 6 weight parts water and 0.55 weight parts alkylpolyglycolether-phosphoricacidester are homogenized by means of a dissolver and ground in a balling mill (Drais, type Perl Mill PML-V/H) using zircon oxide grinding bodies at a temperature of 40-55° C. until the finished dispersion shows an x₉₉<1.50 μm.

Beech wood pulp (R18=97.5%) was alkalified with lye, which contained 240 g/l NaOH, at 35° C. and pressed to an alkali cellulose fleece. The alkali cellulose fleece was disintegrated, ripened and reacted with CS₂ to form the xanthate. The xanthate was dissolved in a diluted soda lye to give a viscose containing 5.6% cellulose, 6.8% NaOH and 39% CS₂, in relation to the cellulose. The viscose was filtered 4 times and de-aerated. 3% (in relation to the cellulose) of an ethoxylated amine, which acts by inducing a core-sheet-structure, was added to the viscose 1 h before spinning. The viscose was post-ripened to a spinning gamma value of 57. The viscosity equaled 80 ballfall seconds during spinning. The finished flame-resistant dispersion is added to this viscose immediately before spinning. The nozzles used reveal a jet hole diameter of 60 μm. The spinning bath contains 72 g/l of sulphuric acid, 120 g/l of sodium sulphate and 60 g/l of zinc sulphate.

The spinning bath temperature equaled 38° C. The coagulated and in part regenerated plastic thread tow, pale yellow in color, was led via a godet (G1) into a second bath, the temperature of which was 95° C., where it was stretched between G1 and a second godet (G2) by 120%. The final draw-off speed equaled 42 m/min. The tow was cut to staples of 40 mm length which were fully regenerated in diluted sulphuric acid, then washed free of acid with hot water, desulphurated with soda lye, washed again, bleached with diluted sodium hypochlorite solution, washed out again, finished, squeezed and dried.

Example 2

6 weight parts 2,2′-oxybis[5,5-dimethyl-1,3,2-dioxaphosphorinane]2,2′ disulfide, 6 weight parts of water and 0.63 weight parts of carboxymethylated alcohol polyglycolether are processed in an analogous manner to example 1 to a viscose ready for spinning (composition: cellulose 5.9%, NaOH 6.7%, 41% CS₂, in relation to the cellulose, 3.5% ethoxylated amine, in relation to cellulose) and spun into an aqueous spinning bath. The nozzles used reveal a spinneret hole diameter of 50 μm. The spinning bath contains 74 g/l of sulphuric acid, 132 g/l of sodium sulphate and 65 g/l of zinc sulphate.

Example 3

6 weight parts 2,2′-oxybis[5,5-dimethyl-1,3,2-dioxaphosphorinane]2,2′ disulfide, 6 weight parts of water and 1.1 weight parts of ethoxylated phtalic acid are processed in an analogous manner to example 1 to a viscose ready for spinning (composition: cellulose 5.8%, NaOH 6.5%, 40% CS₂, in relation to cellulose, as a modification agent a blend of 2% DMA+1% PEG 2000, always in relation to cellulose) and spun into an aqueous spinning bath.

The jets used reveal a jet diameter of 50 μm. The spinning bath contains 73 g/l of sulphuric acid, 120 g/l of sodium sulphate and 58 g/l of zinc sulphate.

Example 4 (Comparative Example)

A fiber was produced in accordance with the teachings of CN101037812. Since no indication is made in this publication with regard to the wet modulus, the conditions of the example there with the highest wet strength (example 2, 1,52 cN/tex) of the fiber obtained were selected and in accordance with this, the following process conditions were set: cellulose 8.86%, NaOH 6.24%, 31% CS₂, in relation to cellulose. A modifying agent was not added. The viscose was spun at a viscosity of 42 ballfall seconds.

The high phosphorous contents indicated in this publication could not be verified. To get acceptable strengths, several optimization tests were performed in the conditions indicated with different contents of flame-resistant agent. The properties indicated could only be attained with the reduction to a phosphorous (P) content of 2.1 weight percentage, in relation to cellulose.

The nozzles used reveal a nozzle hole diameter of 60 μm. The spinning bath contains 115 g/l of sulphuric acid, 330 g/l of sodium sulphate and 45 g/l of zinc sulphate.

Example 5 (Comparative Example)

A fiber was produced according to CN1904156 whereby there the concrete recommended process conditions were set:

Cellulose 8.9%, NaOH 5.2%, 33% CS₂, in relation to cellulose. A modifying agent was not added. The viscose was spun with a viscosity of 55 ballfall seconds.

Likewise the high phosphorous contents indicated in this publication could not be verified. In order to attain acceptable tenacities, several optimization tests were performed with different contents of flame-resistant agent in the conditions named. Likewise in this example it was only possible to attain the given properties as of the reduction to a phosphorous content of 2.1% weight percentage in relation to the cellulose.

The nozzles used reveal a nozzle hole diameter of 60 μm. The spinning bath contains 115 g/l of sulphuric acid, 350 g/l of sodium sulphate and 11 g/l of zinc sulphate. The spinning bath temperature equaled 49° C.

TABLE 1 fiber data BISFA wet P Titer FFk FDk modulus content Usability Fiber (dtex) (cN/Tex) (%) (cN/tex) (%) value Example 1 1.7 28.7 13.3 5.2 3.5 18.2 Example 2 1.7 28.8 14.1 5.3 3.5 18.6 Example 3 1.7 27.3 13.5 5.1 3.5 17.9 Example 4 2.2 18.3 20.2 2.0 2.1 4.2 (comparison) Example 5 2.4 18.5 19.3 1.8 2.1 3.8 (comparison)

The comparison of the fiber properties shows very clearly that flame-resistant viscose fibers which were produced according to the standard viscose conditions in accordance with the examples 4 and/or 5, have clearly poorer usability values than those produced in accordance with the invention. 

1. A flame-resistant regenerated cellulose fiber for textile applications, wherein said fiber comprises an incorporated flame resistant substance comprised of a particle-shaped phosphorous compound wherein said fiber has a usability value of between 6 and
 35. 2. The flame-resistant fiber according to claim 1, wherein said fiber comprises at least 2.8% of phosphorous in relation to cellulose.
 3. The flame-resistant fiber according to claim 1 or 2, wherein the phosphorous compound is 2,2′-oxybis[5,5-dimethyl-1,3,2-dioxaphosphorinane]2,2′ disulfid(I).
 4. The flame-resistant fiber according to claim 1 or 2, having a BISFA wet modulus (B_(m))≧0.5·(√T)·10/T and an elongation of 5% in the wet condition.
 5. The flame-resistant fiber according to claim 1 or 2, wherein the flame-resistant substance has a particle size distribution at X₅₀ less than 1.0 μm and x₉₉ less than 5.0 μm.
 6. The flame-resistant fiber according to claim 1 or 2, wherein the flame-resistant substance originates from a dispersion and wherein said dispersion comprises a dispersing agent selected from the group consisting of modified polycarboxylates, water-soluble polyester, alkyletherphosphates, end-capped nonoxynols, recinus oil alkoxylester and carboxymethylated alcoholpolyglcolether.
 7. A yarn comprising the fiber according to claim 1 or
 2. 8. A fabric comprising the fiber according to claim 1 or
 2. 9. A process for the production of a flame-resistant regenerated cellulose fiber for textile applications which comprises (a) spinning viscose with a content of 4 to 7% cellulose, 5 to 10% NaOH, 36 to 42% (in relation to cellulose) carbon disulphide and 1 to 5% (in relation to cellulose) of a modification agent into a spinning bath; and (b) drawing off of coagulated threads, wherein the viscose has a spinning gamma value of 50 to 68 and a spinning viscosity of 50 to 120 ballfall seconds; and that the temperature of the spinning bath equals 34 to 48° C., characterized in that 1) an alkali ratio (=cellulose concentration/alkali content) of the viscose ready for spinning equals 0.7 to 1.5; 2) the following spinning bath concentrations are used: i) H₂S0₄=68-90 g/l ii) Na₂S0₄=90-160 g/l iii) ZnS0₄=30-65 g/L; 3) the drawing off from the spinning bath takes place at a speed between 15 and 60 m/min and 4) a particle shaped phosphorous compound in the form of a pigment dispersion is incorporated during spinning as a flame-resistant substance.
 10. The process according to claim 9, wherein an amount of the flame-resistant substance is incorporated to result in a finished fiber comprising at least 2.8% of phosphorous, in relation to cellulose.
 11. The process according to claim 9, wherein the phosphorus compound is 2,2′-oxybis[5,5-dimethyl-1,3,2-dioxaphosphorinane]2,2′ disulphide (I).
 12. The process according to claim 9, wherein the pigment dispersion comprises between 10 and 50% of the flame-resistant substance with an average particle size (x₉₀) less than 1.0 μm and a maximum particle size (X₉₉) less than 5.0 μm, and between 1.5 and 20% of a dispersing agent.
 13. The process according to claim 12, wherein the dispersing agent to disperse the flame-resistant substance in the pigment dispersion, and wherein the dispersing agent is selected from the group consisting of modified polycarboxylates, water-soluble polyester, alklyetherphosphates, end-capped nonoxynols, recinus oil alkoxylester and carboxmethylated alcoholpolyglycolether.
 14. The flame-resistant regenerated cellulose fiber according to claim 1, wherein said fiber has a usability value of between 8 and
 35. 15. The flame-resistant regenerated cellulose fiber according to claim 14, wherein said fiber has a usability value of between 10 and
 35. 16. The flame-resistant fiber according to claim 2, wherein said fiber comprises between 3.2% and 6.0% of phosphorous in relation to cellulose.
 17. The flame-resistant fiber according to claim 2, wherein said fiber comprises between 3.5% and 6.0% of phosphorous in relation to cellulose.
 18. The process according to claim 10, wherein the amount of the flame-resistant substance incorporated results in a finished fiber comprising between 3.2% and 6.0% of phosphorous in relation to cellulose.
 19. The process according to claim 18, wherein the amount of the flame-resistant substance incorporated results in a finished fiber comprising between 3.5% and 6.0% of phosphorous in relation to cellulose. 